The invention concerns a method of manufacturing bands or loops of steel with a device including two separate drums with parallel axes, one of the axes stationary and the other transversely variable.
Loops of steel are preferably manufactured from a coil or from several sheets welded together. Once the coil has been uncoiled or the several sheets welded into strips, the length of the desired loop is marked on the tensioned strip with a measuring tape and square and the strip cut with manual or mechanical shears. The strips can be up to 30 m long or longer. At such lengths the longitudinal edges will have tolerances of 5 mm due to the measuring tape's imprecision, to discrepancies in angular measurement, and in particular to inherent distortions in the extended but not tensioned strip.
The accordingly trimmed strip is now welded together into a loop. The strip is wrapped loose around two drums and its ends aligned and secured on a welding surface with the transverse edges in contact or slightly apart depending on what kind of welding is employed. The ends of the strip remain tensioned on the surface during the welding process.
The welded loop is ejected straight. The axis of one drum remains stationary while the other is displaced by an all purpose piston-and-cylinder mechanism until the tension on the loop is approximately 50 N/mm.sup.2. The tensioned loop is now turned several times around the powered drum. Due to the aforesaid considerable tolerances in the longitudinal edges of the extended strip and to its being welded without being uniformly tensioned, the loop may to run off the drums. To prevent this from occurring, one end of the variable drum is tensioned until the strip travels straight. In this state, in which the tensions in the strip are unequal and the axes of the drums are not parallel, the deviation from the straight is measured during one revolution of the strip.
Such strips are controlled in application by sensing the longitudinal edge of the strip and briefly and alternately adjusting the variable drum axis to keep the strip from running off the drum. The strip's inherent uneven tension has additional control tensions imposed over it. It is precisely the uncompensated tension at both edges that decreases the life of such a loop.